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      1 //===- PhiValues.h - Phi Value Analysis -------------------------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // This file defines the PhiValues class, and associated passes, which can be
     10 // used to find the underlying values of the phis in a function, i.e. the
     11 // non-phi values that can be found by traversing the phi graph.
     12 //
     13 // This information is computed lazily and cached. If new phis are added to the
     14 // function they are handled correctly, but if an existing phi has its operands
     15 // modified PhiValues has to be notified by calling invalidateValue.
     16 //
     17 //===----------------------------------------------------------------------===//
     18 
     19 #ifndef LLVM_ANALYSIS_PHIVALUES_H
     20 #define LLVM_ANALYSIS_PHIVALUES_H
     21 
     22 #include "llvm/ADT/DenseMap.h"
     23 #include "llvm/ADT/DenseSet.h"
     24 #include "llvm/ADT/SetVector.h"
     25 #include "llvm/ADT/SmallVector.h"
     26 #include "llvm/IR/PassManager.h"
     27 #include "llvm/IR/ValueHandle.h"
     28 #include "llvm/Pass.h"
     29 
     30 namespace llvm {
     31 
     32 class Value;
     33 class PHINode;
     34 class Function;
     35 
     36 /// Class for calculating and caching the underlying values of phis in a
     37 /// function.
     38 ///
     39 /// Initially the PhiValues is empty, and gets incrementally populated whenever
     40 /// it is queried.
     41 class PhiValues {
     42 public:
     43   using ValueSet = SmallSetVector<Value *, 4>;
     44 
     45   /// Construct an empty PhiValues.
     46   PhiValues(const Function &F) : F(F) {}
     47 
     48   /// Get the underlying values of a phi.
     49   ///
     50   /// This returns the cached value if PN has previously been processed,
     51   /// otherwise it processes it first.
     52   const ValueSet &getValuesForPhi(const PHINode *PN);
     53 
     54   /// Notify PhiValues that the cached information using V is no longer valid
     55   ///
     56   /// Whenever a phi has its operands modified the cached values for that phi
     57   /// (and the phis that use that phi) become invalid. A user of PhiValues has
     58   /// to notify it of this by calling invalidateValue on either the operand or
     59   /// the phi, which will then clear the relevant cached information.
     60   void invalidateValue(const Value *V);
     61 
     62   /// Free the memory used by this class.
     63   void releaseMemory();
     64 
     65   /// Print out the values currently in the cache.
     66   void print(raw_ostream &OS) const;
     67 
     68   /// Handle invalidation events in the new pass manager.
     69   bool invalidate(Function &, const PreservedAnalyses &,
     70                   FunctionAnalysisManager::Invalidator &);
     71 
     72 private:
     73   using ConstValueSet = SmallSetVector<const Value *, 4>;
     74 
     75   /// The next depth number to be used by processPhi.
     76   unsigned int NextDepthNumber = 1;
     77 
     78   /// Depth numbers of phis. Phis with the same depth number are part of the
     79   /// same strongly connected component.
     80   DenseMap<const PHINode *, unsigned int> DepthMap;
     81 
     82   /// Non-phi values reachable from each component.
     83   DenseMap<unsigned int, ValueSet> NonPhiReachableMap;
     84 
     85   /// All values reachable from each component.
     86   DenseMap<unsigned int, ConstValueSet> ReachableMap;
     87 
     88   /// A CallbackVH to notify PhiValues when a value is deleted or replaced, so
     89   /// that the cached information for that value can be cleared to avoid
     90   /// dangling pointers to invalid values.
     91   class PhiValuesCallbackVH final : public CallbackVH {
     92     PhiValues *PV;
     93     void deleted() override;
     94     void allUsesReplacedWith(Value *New) override;
     95 
     96   public:
     97     PhiValuesCallbackVH(Value *V, PhiValues *PV = nullptr)
     98         : CallbackVH(V), PV(PV) {}
     99   };
    100 
    101   /// A set of callbacks to the values that processPhi has seen.
    102   DenseSet<PhiValuesCallbackVH, DenseMapInfo<Value *>> TrackedValues;
    103 
    104   /// The function that the PhiValues is for.
    105   const Function &F;
    106 
    107   /// Process a phi so that its entries in the depth and reachable maps are
    108   /// fully populated.
    109   void processPhi(const PHINode *PN, SmallVectorImpl<const PHINode *> &Stack);
    110 };
    111 
    112 /// The analysis pass which yields a PhiValues
    113 ///
    114 /// The analysis does nothing by itself, and just returns an empty PhiValues
    115 /// which will get filled in as it's used.
    116 class PhiValuesAnalysis : public AnalysisInfoMixin<PhiValuesAnalysis> {
    117   friend AnalysisInfoMixin<PhiValuesAnalysis>;
    118   static AnalysisKey Key;
    119 
    120 public:
    121   using Result = PhiValues;
    122   PhiValues run(Function &F, FunctionAnalysisManager &);
    123 };
    124 
    125 /// A pass for printing the PhiValues for a function.
    126 ///
    127 /// This pass doesn't print whatever information the PhiValues happens to hold,
    128 /// but instead first uses the PhiValues to analyze all the phis in the function
    129 /// so the complete information is printed.
    130 class PhiValuesPrinterPass : public PassInfoMixin<PhiValuesPrinterPass> {
    131   raw_ostream &OS;
    132 
    133 public:
    134   explicit PhiValuesPrinterPass(raw_ostream &OS) : OS(OS) {}
    135   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
    136 };
    137 
    138 /// Wrapper pass for the legacy pass manager
    139 class PhiValuesWrapperPass : public FunctionPass {
    140   std::unique_ptr<PhiValues> Result;
    141 
    142 public:
    143   static char ID;
    144   PhiValuesWrapperPass();
    145 
    146   PhiValues &getResult() { return *Result; }
    147   const PhiValues &getResult() const { return *Result; }
    148 
    149   bool runOnFunction(Function &F) override;
    150   void releaseMemory() override;
    151   void getAnalysisUsage(AnalysisUsage &AU) const override;
    152 };
    153 
    154 } // namespace llvm
    155 
    156 #endif
    157